This invention relates in general to heat exchanger constructions and, more particularly, to hosing for embedding in a slab of concrete, asphalt and other materials to circulate a heat transfer fluid to provide for heat exchange.
It is often desired to heat surfaces such as driveways, parking lots, roadways and sidewalks to remove or to prevent the accumulation of ice and snow from the surface. Heating of interior surfaces such as floors, walls, or ceilings may also be desired to provide a method of heating an area such as a room by radiant heat. Various methods have been employed to provide such heating yet each suffers from one or more deficiencies.
Electric resistance wires embedded in the concrete slab have been frequently used as one method of providing head exchange because the wires are easily installed. These wires, however, are fragile and are likely to break as the concrete slab inevitably settles. Repair of these breaks is often time consuming as the exact location of the breakage is difficult to determine. The heat flux emitted by the wires is also limited by the ability of the relatively small surface area of the wires to conduct heat to the surrounding matrix without the insulating materials covering the wire failing from overheating. The materials used to electrically insulate the wires are also very brittle and subject to corrosion from such common materials as road salt.
Tubes have also been embedded in slabs of concrete and other materials to circulate a heat transfer fluid which warms the surrounding concrete. Conventional heat exchanger tubing is also prone to breakage resulting from settling of. the slab, freezing of the heat transfer fluid, and corrosive attack by chemicals seeping through the slab. The tubing may also be subject to corrosive attack by the heat transfer fluid.
Breakage of the tubing causes leakage of the heat transfer fluid and may result in significant damage to the building and its furnishings. Pinpointing the points of breakage is difficult because the heat transfer fluid may seep through cracks in the slab and surface at a location remote from the point of breakage. The difficulty in locating the tubing once embedded in the slab also presents problems when penetration of the slab is required such as when repairs to the slab are to be effected or equipment bolted or otherwise anchored to the slab.
Tubes constructed from iron, copper or other metals, in addition to being expensive to install, are unsatisfactory in asphalt slabs because of the significant difference in the thermal expansion between the metal and asphalt. Repeated cycles of temperature change often result in the expanding metal to cause cracking of the asphalt, thus exposing the metal tubes to corrosion and weakening.
Plastic tubes which allow atmospheric oxygen to enter the system are unsatisfactory as the oxygen results in severe corrosion of the pumps, boilers and other heat exchanger components. Plastic tubing is also subject to corrosive attack by petroleum distillates, solvents, cleaning fluids and other chemicals that seep through cracks which develop in the concrete as it ages. Some types of plastic tubes are also subject to complete failure at elevated temperatures which may occur due to malfunctioning of heat exchangers or boilers. Plastic tubes are also subject to premature failure in hydronic radiant heating systems due to the continuous flow of hot water through the system that leaches out both the plasticizing agents that maintain the flexibility of the piping, and the anti-oxidants that maintain the strength of the piping. As these agents are removed, many types of plastic tubing, including the most common, polybutylene, become increasingly weakened and embrittled with use.